Mobile phone carriers, buckling under the load that smartphone users put on data networks, are implementing changes designed to reduce the pain.

In the early days of smartphone adoption, unlimited data plans were common. As Sprint advertises, its unlimited plan is the only one left that doesn’t slow down subscribers’ connections once more than 2GB of data is used.

Verizon Wireless and AT&T stopped offering unlimited plans to new customers a year ago, but Verizon is now taking it a step further. At the J.P. Morgan Technology, Media and Telecom conference, CFO Fran Shammo said that even renewing customers who buy a new subsidized device would no longer receive unlimited data transfer.

The change comes as Verizon plans to introduce “data share” plans, in which a certain amount of data transfer is allocated to an account. Currently, each smartphone in a family plan pays its own data service fee; under the new model, that fee and the data would be shared among all members of the family plan.

Current unlimited plans will remain in effect until subscribers upgrade to a new phone or 4G plan, but Verizon is even encouraging present customers to “Unthink Unlimited.” Most subscribers use less than 2GB of mobile data transfer per month, the company’s web site says.

According to USA Today, AT&T wants to reduce data usage below its own imposed limits by transferring subscribers onto open Wi-Fi networks when possible. Users are automatically switched to Wi-Fi inside Starbucks stores, Times Square, Rockefeller Center, and 20 public parks in and around New York, as well as in hot spots in San Francisco and Charlotte.

Sprint also plans automatic switching, but first will implement a feature that simply alerts smartphone users that a Wi-Fi hot spot is nearby, the USA Today article said.

The switch is seamless as long as Wi-Fi is enabled on users’ phones. A standard called Passpoint from the Wi-Fi Alliance industry group allows devices to automatically log on to an access point that has been certified as trustworthy and secure.